In order to save time and labor for applying stamp ink on a stamping surface every time a stamp or stamping plate is impressed, a stamp has been known which has a stamping material made of a rubber sponge having open cells and allows the material to previously occlude ink. For producing the stamp, a producing process of the stamp is disclosed in Japanese patent Application Laid-Open Sho 60 No.193686 in which other part than the impress image forming portion on the sponge surface is pressed and cured to in concave state by hot emboss-forming, so that the convex portion of the sponge may serve as an ink occluding portion for producing the impress image forming portion. Japanese Patent Application Laid-Open Sho-50 No.155434 also discloses a method in which a porous material is pressed against a similar heated plate. These methods, however, require a mold for the heated plate and time and labor for engraving or etching characters, signs, patterns etc. on the die.
Japanese Patent Application Laid-Open Sho-57 No.136652 as well as Japanese Patent Application Laid-Open Sho-49 No.7003, disclose a method of producing a printing plate comprising the steps of: applying a photopolymeric liquid resin on the surface of a stamp-piece made of sponge; placing a positive sheet over the top of the stamp-piece; irradiating the stamp-piece from above with ultraviolet rays to cause a photopolymeric reaction; and washing out the unconverted resin. A similar method using a film negative is disclosed in Japanese Utility Model Application Laid-Open Sho-52 No.71710. Each of these methods, however, has a drawback, such as, for example indulges complicated steps such as preparing a film negative or positive, application of resin, photopolymerization, rinsing and so on. Also, a reference to preparation of a printing surface using a stamp-piece made of sponge is written in Japanese Patent Application Laid-Open Hei 3 No.96383. Further, Japanese Utility Model Application Laid-Open Sho-50 No.41620 shows a method of preparing an original by decomposing a manuscript material with a screen in order to create a stamp of a photograph or a design having gradations in tone.